Mutant proteins of human DNA topoisomerase I

ABSTRACT

Mutant proteins of human DNA topoisomerase I having an amino acid sequence in which tyrosine at the 592nd position of human DNA topoisomerase I is lacking or replaced with phenylalanine and which contains at least 30 amino acids in succession of the amino acid sequence subsequent to the 542nd amino acid of human DNA topoisomerase I. 
     Above described mutant proteins react with anti-Scl-70, antibody in the sera of autoimmune disease patients of diffuse scleroderma and can be produced by genetic engineering using E. coli, and therefore they are useful as a diagnostic agent of scleroderma.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel mutant proteins of human DNA topoisomerase I. These mutant proteins are preferably produced by genetic engineering and useful for a diagnosis of autoimmune diseases and for analysis of topological interconversion of genes.

2. Description of the Prior Art

The autoantibodies against various nuclear antigens are detected in the sera of patients with autoimmune diseases, and it is possible to diagnose autoimmune diseases by detecting these autoantibodies.

It is known that, among these autoantibodies, the autoantibodies against a nuclear antigen, Scl-70 having a molecular weight of 70 kD, are detected in sera of many patients with an autoimmune disease named diffuse scleroderma. In recent years it has been demonstrated that Scl-70 is a 70 kD-molecular-weight protein of the C-terminal fragment of DNA topoisomerase I (J. H. Sero et al., 1986, Science, Vol. 231, pp. 737-740). DNA topoisomerases catalyze the breaking and rejoining of DNA strands in a way that allows the strands to pass through one another, thus altering the topology of DNA. There exist two kinds of DNA topoisomerases, Type I and Type II. Type I cleaves a single chain DNA while Type II cleaves a double-chain DNA.

The topological interconversion is brought about by these DNA topoisomerases I and II, which are necessary for the transcription from DNA to RNA and for replication of DNA. These DNA topoisomerases I and II are also essential proteins for cell proliferation and functional maintenance such as protein synthesis. In particular, Scl-70, namely, 70 kD-molecular-weight protein of the C-terminal fragment of human DNA topoisomerase I, is useful for a diagnosis of autoimmune diseases such as diffuse scleroderma. However, it is not commercially feasible to extract and purify human DNA topoisomerase I from natural materials due to scarce content of the protein in organisms. It is preferably by genetic engineering that the enzyme is practically produced.

The cDNA of human DNA topoisomerase I was cloned by P. D'Arpa in 1988 (Proc. Natl. Acad. Sci., USA, Vol. 85, pp. 2543-2547). However, production of a sufficient amount of the targeted recombinant protein was unsuccessful. A trial was made to express human DNA topoisomerase I by integrating it into a conventional expression vector in E. coli according to conventional genetic engineering methods. A large amount of the enzyme production in E. coli caused inhibition of the transcription of the E. coli DNA itself and caused inhibition of DNA replication. Thus, growth of the E. coli was inhibited, and death of the E. coli was observed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for mutant proteins of human DNA topoisomerase I which are preferably produced by genetic engineering. It is estimated that the active site of human DNA topoisomerase I is tyrosine (Tyr) at amino acid 723 (Proc. Natl. Acad. Sci., 1989, Vol. 86, pp. 3559-356). Moreover, a mutant protein lacking 95 amino acids at terminal fragments and 723-phenylalanine (Phe) whose active also inhibited the growth of E. coli, and failed to produce a sufficient amount of the mutant protein. Then, upon producing a mutant protein of human DNA topoisomerase I (FF mutant hereinafter, shown in SEQ ID NO.:1 of the Sequence Listing) by substituting Tyr at the 592nd amino acid with Phe, FF mutant reacted sufficiently with anti-Scl-70, autoantibodies in the sera of autoimmune disease patients. In addition the production of FF mutuant in E. coli was found very high, which led to the completion of the invention.

Further, it was found that the mutant protein of human DNA topoisomerase I which consists of Ala at the 96th amino acid to Phe at the 765th amino acid, Tyr at the 723rd (i.e., the amino acid of the wild type protein) and substituting Tyr at the 592nd amino acid with Phe (FY mutant hereinafter) was recovered in a large quantity at 4 to 5 hours after induction of transformed E. coli by reagents. FY mutant as well as FF mutant has antigenicity and is produced from the cultured E. coli, and can be utilized as a diagnostic reagent.

The fragment peptide of human DNA topoisomerase I which contains at least 30 and preferably 40 or more amino acids in succession from the amino acid sequence from proline (Pro) at the 542nd, amino acid if Tyr at the 592nd amino acid of human DNA topo-isomerase I is lacking or replaced with Phe, contains epitopes which anti-Scl-70 autoantibody recognizes (refer to Example 5), and can also be utilized as a diagnostic reagent. Examples of peptide fragments are also contained in the mutant proteins of this invention. The ES mutant protein (ES mutant) consists of Ala at the 96th amino acid through Arg at the 590th amino acid of each wild type human DNA topoisomerase I. The SR mutant protein (SR mutant) consists of Thr at the 591st amino acid through Phe at the 765th amino acid and the Tyr residues at the 592nd and the 723rd amino acids which are replaced with Phe, and the mutant protein consisting of Pro at the 542nd amino acid through Phe at the 765th amino acid and the Tyr at the 592nd and the 723rd amino acid which are replaced with Phe are examples, in addition to FF mutant and FY mutant.

Further, the mutant proteins of human DNA topoisomerase I and their fragments according to the present invention also include those of the converted amino acids by deficiency, replacement addition or combination thereof provide that change in its antigenicity is not caused.

By using either FF mutant or FY mutant of the present invention, an antoimmune disease assay kit can be produced according to a conventional method. The analysis methods that can be used are ELISA, RIA and Latex Agglutination wherein an autoantibody in a specimen is detected by binding either FF mutant or FY mutant on an immobilized phase of plastic or glass and using these as antigens according to immunological antigen-antibody reaction. Also, the autoimmune disease diagnosed according to the present invention can be used for diagnosis of autoimmune diseases in which autoantibodies against Scl-70 are detected in the sera. A representative autoimmune disease is diffuse scleroderma.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plasmid map of pSEM•FF and pSEM•FY.

FIG. 2 is a photo of the electrophoresis pattern of the FF mutant produced by E. coli carrying a the FF mutant plasmid.

FIG. 3 is a photo of the electrophoresis pattern of the reaction of the FF mutant proteins with anti-Scl-70 antibody in the sera of patient.

FIG. 4 is a plasmid map encoding Scl-70 protein (FF mutant derived from PSEM•FF, a mutant protein (ES mutant) derived from pSEM•ES and a mutant protein (SR mutant) derived from pSEM•SR.

FIG. 5 is a photo of the electrophoresis pattern of the FY mutant produced in E. coli carrying pSEM•FY.

FIG. 6 is a photo of the electrophoresis pattern of the FY mutant.

EXAMPLE

This invention shall be more illustratively explained by way of the following Examples.

Example 1 Cloning of cDNA encoding human DNA topoisomerase I

1. According to the method by Benton Davis et al. (Science 1977, Vol. 196, p. 180), a single colony of E. coli LE392 (purchased from Promega Co.) was cultured for 5 hours in LS culture medium (10 g polypeptone, 5 g yeast extract, 2.5 g NaCl/1 L) which were added 0.02% maltose and 10 mM MgSO₄, and 0.3 ml of the culture was distributed into a test-tube, and 40 μl of human placenta-derived cDNA library HL1008 (purchased from Clontech Lab. Co.) equivalent to 3.5×10⁵ P.F.U. (plaque forming unit) diluted with λdil (86 mM NaCl, 100 mM Tris-HCl pH 7.4, 0.001% gelatin, 1 mM MgCl₂) was added and then added with 10 ml λtop agarose at 60° C. (BACTOTRYPTONE 10 g, NaCl 5 g, agarose 5 g/L:10 mM MgSO₄), after agitation flown onto LS agarose plate (15 cm diameter). After the agarose was solidified, the plate was cultured in an incubator at 37° C. for 6 hours, and then moved to 4° C.

2. For purposes of transferring the plaque developed on the agarose to a nitrocellulose filter (purchased from Schleicher & Schwell Co.), the filter was placed on the agarose, and pulled off the agarose after 2.5 minutes, and dried for 10 minutes at room temperature. Then, the filters were treated for 2.5 minutes each with alkali denaturing solution (0.5N NaOH/1.5M NaCl), neutralizing solution (0.5M Tris-HCl, pH 7.5) and 2×SSC (0.15M NaCl, 0.015M Na₃ citrate-2H₂ O), and dried at 37° C. for 30 minutes. The filters were then further heat-treated in an oven at 80° C. for 2 hours.

3. The above described filters were soaked with a prehybridization solution (50% formamide, 6×SSC, 5×Denhardt, 50 mM Hepes pH 7.0, 80 μg/ml ssDNA) at 40° C. for 4 to 5 hours. Then, by using 12 ml of the same solution containing 1×10⁷ cpm of probe labelled with ³² p, 10 sheets of filters were sealed in a hybridization bag, incubated at 40° C. for 20 hours. After the incubation, the filters were out, and after removed washed once with 2×SSC at room temperature for 15 minutes, and 3 times with 0.1×SSC/0.1% SDS at 42° C. for 15 minutes, were then air-dried and auto-radiographed.

4. Labelling of probe

70 μCi (2.6 MBq) of γ³² ATP and T4 kinase were added to 50 pmole of synthesized DNA, reacted at 37° C. for 30 minutes in a reaction mixture (70 mM Tris-HCl, pH 7.6, 10 mM MgCl₂, 5 mM DTT, 1 mM EDTA). Free isotope was removed by a span column of Sephadex G50 (fine) (purchased from Pharmacia AB).

5. Isolation of single plaque

A plaque located at a position of signals on the autoradiogram was picked suspended in 500 μl of γdil, diluted as in Example 1-1 to obtain the plaque. The procedures as described in Example 1-2 and were repeated, and a single plaque was isolated.

6. Detection of insert size of phage DNA from a plaque

The isolated plaque was suspended in 200 μl of SM buffer (100 mM NaCl, 8 mM MgSO₄, 50 mM Tris-HCl, pH 7.5, 0.01% gelatin), diluted and use to infect 400 times, E. coli Y1090 (purchased from Stratagene Co.) to obtain a novel plaque. The novel plaque was suspended in 200 μl of SM buffer, to prepare a phage solution for PCR. 4 μl of the phage containing solution was added to 20 μl of PCR buffer (1 μM primer, 0.2 mM dNTP, 67 mM Tris-HCl, pH 8.8, 1 mM β-ME, 16.6 mM (NH₄)₂ SO₄). The Reaction mixture was heated once for 5 minutes at 95° C., and then, for 35 cycles, the reaction mixture was heated for 1 minute at 94° C., then 2 minutes at 55° C. and then 3 minutes at 72° C. The size of the DNA obtained from the PCR reaction was examined by electrophoresis with 0.8% agarose gel, using 1/5 volume of the reaction mixture. Further, 3 μl of the solution after the PCR reaction was digested with Hind III, EcoRV, BstXI and XhoI, and then subjected to electrophoresis in the same manner as shown above, and the migration pattern was examined.

7. Preparation of phage DNA

After each 5 μl, 10 μl and 20 μl of the phage solution containing Scl-70 cDNA was used to infect 100 μl of E. coli LE 392. The bacteria-phage mixture was spread on agarose plate (8 cm in diameter), and incubated at 37° C. overnight. 4 ml of SM buffer was added per plate, which stood at room temperature for 2 to 3 hours. The buffer was transferred to a centrifugal tube of 15 ml, and centrifuged at 3,000 rpm for 10 minutes. 20 μg/ml of RNase and 20 μg/ml of DNase were added to the supernatant, and incubated at 37° C. for 30 minutes. The solution was centrifuged at 35,000 rpm at 4° C. for 45 minutes using a Hitachi RPS 40T rotor. The precipitate was suspended in 600 μl of sterilized distilled water, then transferred to an Eppendorf tube, and centrifuged for 5 minutes at 4° C. at 15,000 rpm. Next 100 mM of EDTA and 0.2% of SDS to 500 μl was added to the supernatant. The solution was extracted once with the same volume of phenol saturated with TE (10 mM Tris-HCl, pH 7.5, 1 mM EDTA), twice with 1/2 volume chloroform. Then, 250 mM NaCl and two volumes of ethanol were added to the solution, then incubated at -80° C. for 5 to 10 minutes, centrifugated at 15,000 rpm for 15 minutes and the precipitate was recovered. The precipitate was dissolved in 200 μl of sterilized distilled water resulting in a phage DNA solution.

8. Sub-cloning

60 μl of the phage DNA solution was digested with EcoRI in the 200 μl reaction mixture, extracted with phenol, fractionated by electrophoresis in 0.8% agarose, and a 3.5 kb EcoRI fragment was obtained by glass milk method. Namely, 200 μl of agarose fragment containing DNA was dissolved with 600 μl of NaI solution, by incubating at 55° C. for 3 minutes, 5 μl of the glass milk was added and incubated for 5 minutes on ice. The glass milk was precipitated by centrifugation at 15,000 rpm for 10 seconds, then the glass milk was washed with an ethanol/salt base washing solution for 2 to 3 times, 10 μl of water was added to the precipitate, incubated at 55° C. for 3 minutes. The DNA was recovered as an aqueous solution after centrifugation. This procedure was performed by using GENECLEAN Kit II (purchased from Funakoshi Co., Ltd.) (Glass Milk Method).

85 ng (1 μl) of pUC118 was added to 15 ng (equivalent to 3 μl) of the DNA, then 16 μl of TAKARA ligation A buffer (purchased from Takara Shuzo Co., Ltd.) and 4 μl of B buffer was added to the DNA solution, and incubated at 16° C. for 30 minutes.

10 μl of the ligation reaction mixture was mixed with 200 μl of Competant Cell (DH5α:purchased from Toyobo Co.), and stored on ice for 30 minutes. Then, after the mixture was incubated at 42° C. for 2 minutes, 800 μl of LS was added and incubated at 37° C. for 60 minutes. The upper solution was spread on an ampicillin plate (containing 0.1 mM Xgal 0.004% of isopropyl-1-thio-β-D-galactoside (IPTG)), and incubated at 37° C. overnight. The obtained clone p66 was subjected to further experiments.

Example 2 Production of FF Mutant Carrying Plasmid (pSEM•FF)

1. PCR Amplification of Fragment I

By using each 1 μM of Scl-70 PR₁ primer (SEQ ID NO.:2) and Scl-70 PF₁ primer (SEQ ID NO.:3), a PCR reaction mixture (200 μl) containing 0.5 ng of Scl-70/pUC118 clone p66-derived EcoRI/EcoRV 2.1 kb fragment was reacted at 95° C. for 1 minute, then at 55° C. for 2 minutes, and then at 72° C. for 2 minutes, and the reaction cycle was repeated 40 times. After completion of the reaction, the reaction mixture was extracted twice with 100 μl chloroform water saturated phenol and chloroform, and once with 200 μl of chloroform. Then, 200 mM of NaCl and 2.5 volume of ethanol was added to the reaction mixture, and stored at -20° C.

2. Digestion with Restriction Enzyme and Sub-Cloning

After digesting the PCR amplified fragment with Avr II and Nhe I, the fragment was phenol extracted and precipitation with ethanol were performed as described above. 6 μg of Scl-70/pUC118 clone p66 plasmid was digested with Avr II and Nhe I, Avr II-Nhe I fragment was fractionated by electrophoresis with 0.8% agarose gel, and the remaining 6.9 kb vector fragment was isolated by the glass milk method. After 32 ng of the vector fragment was ligated with 100 ng of a PCR amplified fragment by TAKARA ligation kit, 10 μl of the ligation mixture was mixed with 200 μl of competent cells of DH5α and the transformation was performed as described above. The nucleotide sequence of the obtained clone was analyzed by Sanger Method (Proc. Natl. Acad. Sci., 1977, Vol. 74, p. 5463) with N8 primer (SEQ ID NO.:4), and the clone, in which the 723rd amino acid Tyr therefore was substituted with Phe was named p66e.

3. Amplification of PCR Fragment II and Sub-Cloning

By using PF₂ primer (SEQ ID NO.:5) and PR₂ primer (SEQ ID NO.:6), after the PCR reaction was performed in 0.75 mM of MgCl₂ as with fragment I, the product was extracted with phenol and precipitated with ethanol, and the fragment was recovered. The fragment was digested with Nhe I and Spl I, and subjected to phenol extraction and ethanol precipitation. On the other hand, the p66e vector backbone was obtained by digesting with Nhe I and Spl I, and then, phenol extraction and ethanol precipitation were carried out. These DNA fragments were fractionated by electrophoresis is an 0.8% agarose gel. The 200 bp of the PCR fragment and the 6.9 kb band of the vector were recovered by the glass milk method. The two isolated DNA fragments were ligated and transformed by using 200 μl of competent cells of XL 1 blue (Strategene Co.). The nucleotide sequence of the resulting clone was analyzed and the clone was named p66FF.

4. Construction of Expression Vector

After digesting 10 μg of p66FF plasmid with Sac I and EcoRV, the 2.2 kb band containing FF mutant gene was fractionated by electrophoresis with an agarose gel, and recovered by the glass milk method. After digesting 35 μg of an expression vector pSEM with Sac I and Sma I, and the vector DNA was recovered in the same manner. After the fragment having FF mutant gene and the vector as described previously was transfected to XL 1 blue with the ligation mixture. Similarly, an expression experiment was performed using the obtained colony (clone) carrying pSEM•FF. pSEM•FF plasmid map is shown in FIG. 1. As shown clearly in FIG. 1, both the 592nd and the 723rd amino acids of pSEM•FF are Phe.

Example 3 Production of FF mutant by E. coli

1. Expression

By using DNA of pSEM•FF, W3110 lac Iq (Hoechst AG) was transformed, and seed clones for an expression experiment were prepared from a single colony. Four independent clones were spread thoroughly on LS plate containing 200 μg/ml ampicillin and stored at 37° C. overnight for cultivation. The bacteria on the plate were collected by a platinum loop, and used to inoculate 3 ml of LS culture medium containing ampicillin, then incubated at 37° C. with shaking for 1.5 hours. Based on the OD₅₅₀ value of the culture, the culture was used to inocutate 20 ml of the culture medium so as to give OD₅₅₀ =0.2, and continued to incubate at 37° C. with shaking. After the value of OD₅₅₀ 0.8 was reached in 2 hours, IPTG was added to give a final concentration of 1 mM. 0, 4 and 18 hours after the addition of IPTG, the culture equivalent to OD₅₅₀ =1.0 was harvested by centrifugation at 15,000 rpm for 2 minutes, suspended in 50 μl of a sample solution (7M urea, 37.5 mM of Tris-HCl, pH 8.8, 1% of SDS, 12.5% of sucrose, 4% of β-mercaptoethanol, 0.5 mg/ml of bromophenol blue), after boiling for 15 minutes, 7 μl was electrophoresed on a 10% polyacrylamide gel. The electrophoresis pattern of Coomassie staining was shown in FIG. 2. An accumulation of 128 kD band was observed after 4 hours of IPTG addition. The bacterial culture used for purification was performed on a 100 ml scale, cultured for 18 to 20 hours after induction, and harvested by centrifuging for 10 minutes at 6,000 rpm by Hitachi RPR 12-1 rotor.

2. Purification

The bacteria was suspended in 10 ml of TEN buffer (50 mM of Tris, pH 7.5, 10 mM of EDTA, 100 mM NaCl), and each of the mixture 1 ml was distributed into each Eppendorf tube, sonicated for ten times of 2 minutes, centrifuged for 10 minutes at 15,000 rpm, and then the precipitate was obtained. The precipitation was washed with TE buffer (100 mM of Tris-HCl, pH 7.5, 1 mM of EDTA) containing 100 mM. After of n-octylglucopyranoside, the precipitate was suspended in 200 μl of 4M urea, after incubated at 37° C. for 1 hour, centrifuged at 15,000 rpm for 20 minutes, and the resulting precipitate was eluted with 200 μl of 7M urea, and prepared as an antigen protein.

Example 4 Production of Deletion Mutant

For purposes of determining the epitope which anti-Scl-70 antibody recognizes, several kinds of deletion mutants were constructed from the DNA fragment encoding a partial Scl-70 containing Ala at the 96th amino acid through C-terminus of wild-type Scl-70 obtained in Example 1. The construction for each of the expression plasmid was made in accordance with Example 2, and the production of these deletion mutant proteins was made in accordance with Example 3. Shown in FIG. 4 is the se- quence of obtained mutants. The following mutuants were obtained: "EH" containing a partial sequence of Ala at the amino acid through Asp at the 483rd amino acid from EcoRI linker site at the 5' side of wild-type Scl-70 to Hind III (EH mutant hereinafter); "EP" containing a partial sequence of Ala at the 96th amino acid through Lys at the 540th amino acid from EcoRI to PpuMI (EP mutant hereinafter); "ES" containing a partial sequence of Ala at the 96th amino acid through Arg at the 590th amino acid from EcoRI to SnaBI (ES mutant hereinafter); and "SR" containing Thr at the 591st amino acid through Phe at the 765th amino acid from SnaBI to the C-terminus and whose 592nd and 723rd amino acids are replaced with Phe (SR mutant hereinafter).

Example 5 Measurement of Anti-Scl-70 Antibody in the Sera of Patients Using FF, ES and SR Mutants

1. Western Blotting

7 μl of FF mutant obtained in Example 3 was electrophoresed in a 10% of SDS polyacrylamide gel, and then was transferred to a nitrocellulose filter and blocked with casein buffer (10 mM of Tris-HClr pH 7.5, 150 mM of NaCl, 0.5% of casein) at 4° C. for 1 hour. After hour reacting at room temperature for 1 hour with the patients' sera diluted 100 times with casein buffer containing 200 μg/ml E coli lysate, washed 4 times with PBS, reacted for 1 hour with rabbit anti-human IgG conjugated with horse radish peroxidase (HRPO), and developed with 4-chloronaphthol. Electrophoresis pattern of the reactant is shown in FIG. 3. 128 kD band and 58 kD band stained with Commassie blue were reacted with the patient's sera. The 58 kD band is considered as a product from the initiation point of transcription.

2. ELISA

Each well of a microtiter plate was coated with 250 ng. of FF mutant obtained in Example 3 and ES and SR mutants obtained in Example 4 at 4° C. overnight, and washed three times with a POD solution (purchased from Behringwerke AG). 50 μl of patients' sera diluted in 100 times with casein buffer containing 200 μg/ml E. coli lysate was added and incubated at 25° C. for 60 minutes. After washing 3 times with the POD solution, anti-human IgG was added to the plate in the same manner as in Example 4-1, and incubated at 25° C. for 60 minutes. Then, TMB (tetramethylbenzidine) was added, and after reacting at 25° C. for 30 minutes, the reaction was stopped by adding 50 μl of 0.5N H₂ SO₄. The absorbance at OD₄₅₀ was measured. The results are shown in Table 1.

                  TABLE 1                                                          ______________________________________                                         Serum No.                                                                      of patient                                                                              ES mutant    FF mutant                                                                               SR mutant                                       ______________________________________                                         1        1.411        1.179    0.227                                           2        1.357        1.443    0.741                                           3        1.251        0.864    0.203                                           4        0.917        1.421    1.001                                           5        0.493        1.157    0.964                                           6        0.705        1.379    1.234                                           7        0.686        1.198    1.036                                           8        1.360        0.973    0.046                                           9        0.750        1.228    0.960                                           10       0.426        0.708    0.408                                           11       2.20         2.20     0.951                                           12       0.385        1.400    1.133                                           13       0.489        0.585    0.029                                           14       0.561        1.158    0.965                                           15       0.457        0.280    0.018                                           16       0.649        1.773    0.772                                           ______________________________________                                    

The ELISA assay was performed by using ES and FF mutants as antigens, and 2 different groups were found out of 16 specimens; 6 specimens had higher or equivalent values in the ES mutant than in the FF mutant, while 10 specimens had higher absorption in the FF mutant compared to the ES mutant. The specimen group which had higher absorption in the FF mutant compared to ES mutant also has higher reactivity with the SR mutant, suggesting that at least two epitopes existed on ES and SR mutants. Consequently, it is considered that the existence of both epitopes can be firmly recognized when the ES and FF mutants are used as an antigen. It is thought that a difference of clinical feature can be suggested by diagnostic results with both antigens.

Example 6 Analysis of EH and EP Mutants by Western Blotting

Out of the deletion mutants obtained in Example 4, the remaining EH, EP and ES mutants of control as analyzed in Example 5 were analyzed for reactivity with anti-Scl-70 autoantibody by Western Blot analysis using the panel patients' sera. The results were marked as "±" showing extremely weak reaction in EH and EP mutants, respectively, while ES mutant, control used also in Example 5 was marked as "++" showing strong reactivity. These results show that the epitopes which anti-Scl-70 autoantibody recognizes exist between Pro of the 542nd amino acid and the 765th amino acid of C-terminal.

Example 7 Production of Plasmid Coding FY Mutant

After obtaining fragment II in the same manner as in Examples 2 and 3, the fragment was digested with Spl I and Nhe I, the 200 bp fragment was subcloned at Nhe I and SplI sites in vector p66, and plasmid p66FY was obtained. Further, the plasmid was subcloned into pSEM3 at Sac I and Sma I sites in the same manner as in Examples 2 and 4, and pSEM•FY was obtained. Shown in FIG. 1 is the plasmid map of pSEM•FY. As clearly shown in FIG. 1, pSEM•FY has Phe at the 592nd amino acid and Tyr at the 723rd amino acid.

Example 8 Production of FY mutant by E. coli

W3110 lacIq strain was transformed with 0.5 ng of pSEM•FY plasmid DNA recovered in XL1 blue, and bacterial lysates were prepared from clones obtained. The clones were spread on LS plate containing 100 μg/ml of ampicillin, and incubated at 37° C. overnight. The bacteria was collected by a platinum loop and pre-cultured in 2 to 3 ml LS culture medium containing ampicillin for 1 to 2 hours. The culture was inoculatd to 15 to 20 ml of the LS culture medium so as to give an OD₅₅₀ =0.2, and cultured for 1.5 to 2 hours. IPTG was added to give a final concentration of 1 mM when the OD₅₅₀ reached 0.8 to 1.0, and cultivation was allowed to continue. The cells equivalent to OD₅₅₀ =1.0 were harvested at 4 hours and 18 hours after IPTG addition, and a portion of these cells were used for enzyme activity in Example 9. Another portion was used for electrophoresis with polyacrylamide gel and Coomassie staining as in Example 3. A photo of the electrophoresis pattern is shown in FIG. 5. The 128 kD band is observed in 4 hours, however, it has disappeared in 18 hours.

Example 9 Enzyme Activity of FY Mutant

1. Preparation of Supernatant (lysate)

The bacteria equivalent to OD₅₅₀ =1.0 is suspended in 300 μl of the sucrose buffer (25% of sucrose, 50 mM of Tris-HCl, pH 8.0, 1 mM of EDTA), washed, and centrifuged at 15,000 rpm for 2 minutes. The precipitate was suspended in 13 μl of the sucrose buffer containing 1 mg/ml lysozyme, and after standing for 2 minutes on ice, the same volume of Brij buffer (10 mM of Tris-HCl, pH 8.0, 0.9% of Brij) was added. After further standing for 2 minutes on ice, 100 mM of KCl was added. And then, after standing for 2 minutes on ice, the supernatant was recovered by centrifugation at 15,000 rpm for 5 minutes.

2. Measurement of Activity

After incubating at 37° C. for 30 minutes, 3 μl of the above supernatant and 200 ng of pUC19 DNA were added in 16 μl of a reaction mixture (50 mM Tris-HCl, pH 8.0, 100 mM KCl, 5 mM DTT, 100 μg/ml BSA). Then 1.5 μg/ml of RNase was added and incubated further for 10 minutes. After incubation, phenol extraction was performed with 8 μl of water saturated phenol and 8 μl of chloroform. 5 μl of loading dye for electrophoresis was added to its supernatant of phenol extraction, incubated at 65° C. for 5 minutes, then electrophoresed in a 0.8% agarose gel. The electrophoresis was performed in TBE buffer (50 mM of Tris-HCl, pH 8.0, 90 mM of boric acid, 1.1 mM of EDTA) at 60V for 3 hours. After electrophoresis, the gel was stained with 0.5 μg/ml of ethidium bromide. A photo of the electrophoresis pattern is shown in FIG. 6.

FIG. 6 shows the result of enzyme activity of the samples at 4 hours and 18 hours after IPTG addition of 6 clones harvested in Example 8. In each lane, pUC19 moves from twisted form I to open circle form II, and thus topoisomerase activity was recognized. These results suggests a possibility of producing recombinant human topoisomerase I in E. coli carrying PSEM•FY mutant proteins.

SEQ ID No.:1 of the Sequence Listing shows an amino acid sequence and the corresponding DNA sequence encoding a mutant protein in which both tyrosine at the 592nd and 723rd amino acid positions of human DNA topoisomerase I are replaced with phenylalanine

The preferable mutant proteins in the present invention shall be more illustratively explained on the basis of the above-mentioned Sequence Listing.

1. A mutant protein (ES mutant) of human DNA topoisomerase I having an amino acid sequence from the 96th to the 590th amino acid in SEQ ID No.:1 of the Sequence Listing.

2. A mutant protein (SR mutant) of human DNA topoisomerase I having an amino acid sequence from the 591st to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing.

3. A mutant protein of human DNA topoisomerase I having an amino acid sequence from the 591st to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing and being replaced with tyrosine at the 723rd amino acid position.

4. A mutant protein (FF mutant) of human DNA topoisomerase I having an amino acid sequence from the 96th to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing.

5. A mutant protein (FY mutant)of human DNA topoisomerase I having an amino acid sequence from the 96th to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing and being replaced with tyrosine at the 723rd amino acid position.

6. A mutant protein of human DNA topoisomerase I having an amino acid sequence from the 542nd to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing.

7. A mutant protein of human DNA topoisomerase I having an amino acid sequence from the 542nd to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing and being replaced with tyrosine at the 723rd amino acid position.

8. A mutant protein of human DNA topoisomerase I having an amino acid sequence from the 1st to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing.

9. A mutant protein of human DNA topoisomerase I having an amino acid sequence from the 1st to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing and being replaced with tyrosine at the 723rd amino acid position.

10. A mutant protein of human DNA topoisomerase I having an amino acid sequence from the 1st to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing, in which the amino acids at the 592nd position and 723rd amino acid position are both lacking.

11. A mutant protein of human DNA topoisomerase I having an amino acid sequence from the 1st to the 765th amino acid in SEQ ID No.:1 of the Sequence Listing, in which one of the amino acids at the 592nd amino acid position and 723rd amino acid position is lacking and the other is replaced with tyrosine. The above-mentioned mutant proteins shall be utilized for the detecting autoantibodies.

Utilized possibility in industry

The mutant protein (FF mutant) of human DNA topoisomerase I provided by the present invention shall be utilized as a detection agent for autoimmune diseases. The mutant protein (FY mutant) of human DNA topoisomerase I, in the same way, shall be utilized for the production of recombinant human topoisomerase.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 7                                                   (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 3645 base pairs                                                    (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: cDNA to mRNA                                               (ix) FEATURE:                                                                  (A) NAME/KEY: CDS                                                              (B) LOCATION: 212..2506                                                        (D) OTHER INFORMATION: /label=FFmutant                                         (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        GAATTCGGGCGCCGCCCGCCCGGCAGTCAGGCAGCGTCGCCGCCGTGGTAGCAGCCTCAG60                 CCGTTTCTGGAGTCTCGGGCCCACAGTCACCGCCGCTTACCTGCGCCTCCTCGAGCCTCC120                GGAGTCCCCGTCCGCCCGCACAGGCCGGTTCGCCGTCTGCGTCTCCCCCACGCCGCCTCG180                CCTGCCGCCGCGCTCGTCCCTCCGGGCCGACATGAGTGGGGACCACCTCCAC232                        MetSerGlyAspHisLeuHis                                                          15                                                                             AACGATTCCCAGATCGAAGCGGATTTCCGATTGAATGATTCTCATAAA280                            AsnAspSerGlnIleGluAlaAspPheArgLeuAsnAspSerHisLys                               101520                                                                         CACAAAGATAAACACAAAGATCGAGAACACCGGCACAAAGAACACAAG328                            HisLysAspLysHisLysAspArgGluHisArgHisLysGluHisLys                               253035                                                                         AAGGAGAAGGACCGGGAAAAGTCCAAGCATAGCAACAGTGAACATAAA376                            LysGluLysAspArgGluLysSerLysHisSerAsnSerGluHisLys                               40455055                                                                       GATTCTGAAAAGAAACACAAAGAGAAGGAGAAGACCAAACACAAAGAT424                            AspSerGluLysLysHisLysGluLysGluLysThrLysHisLysAsp                               606570                                                                         GGAAGCTCAGAAAAGCATAAAGACAAACATAAAGACAGAGACAAGGAA472                            GlySerSerGluLysHisLysAspLysHisLysAspArgAspLysGlu                               758085                                                                         AAACGAAAAGAGGAAAAGGTTCGAGCCTCTGGGGATGCAAAAATAAAG520                            LysArgLysGluGluLysValArgAlaSerGlyAspAlaLysIleLys                               9095100                                                                        AAGGAGAAGGAAAATGGCTTCTCTAGTCCACCACAAATTAAAGATGAA568                            LysGluLysGluAsnGlyPheSerSerProProGlnIleLysAspGlu                               105110115                                                                      CCTGAAGATGATGGCTATTTTGTTCCTCCTAAAGAGGATATAAAGCCA616                            ProGluAspAspGlyTyrPheValProProLysGluAspIleLysPro                               120125130135                                                                   TTAAAGAGACCTCGAGATGAGGATGATGTTGATTATAAACCTAAGAAA664                            LeuLysArgProArgAspGluAspAspValAspTyrLysProLysLys                               140145150                                                                      ATTAAAACAGAAGATACCAAGAAGGAGAAGAAAAGAAAACTAGAAGAA712                            IleLysThrGluAspThrLysLysGluLysLysArgLysLeuGluGlu                               155160165                                                                      GAAGAGGATGGTAAATTGAAAAAACCCAAGAATAAAGATAAAGATAAA760                            GluGluAspGlyLysLeuLysLysProLysAsnLysAspLysAspLys                               170175180                                                                      AAAGTTCCTGAGCCAGATAACAAGAAAAAGAAGCCGAAGAAAGAAGAG808                            LysValProGluProAspAsnLysLysLysLysProLysLysGluGlu                               185190195                                                                      GAACAGAAGTGGAAATGGTGGGAAGAAGAGCGCTATCCTGAAGGCATC856                            GluGlnLysTrpLysTrpTrpGluGluGluArgTyrProGluGlyIle                               200205210215                                                                   AAGTGGAAATTCCTAGAACATAAAGGTCCAGTATTTGCCCCACCATAT904                            LysTrpLysPheLeuGluHisLysGlyProValPheAlaProProTyr                               220225230                                                                      GAGCCTCTTCCAGAGAATGTCAAGTTTTATTATGATGGTAAAGTCATG952                            GluProLeuProGluAsnValLysPheTyrTyrAspGlyLysValMet                               235240245                                                                      AAGCTGAGCCCCAAAGCAGAGGAAGTAGCTACGTTCTTTGCAAAAATG1000                           LysLeuSerProLysAlaGluGluValAlaThrPhePheAlaLysMet                               250255260                                                                      CTCGACCATGAATATACTACCAAGGAAATATTTAGGAAAAATTTCTTT1048                           LeuAspHisGluTyrThrThrLysGluIlePheArgLysAsnPhePhe                               265270275                                                                      AAAGACTGGAGAAAGGAAATGACTAATGAAGAGAAGAATATTATCACC1096                           LysAspTrpArgLysGluMetThrAsnGluGluLysAsnIleIleThr                               280285290295                                                                   AACCTAAGCAAATGTGATTTTACCCAGATGAGCCAGTATTTCAAAGCC1144                           AsnLeuSerLysCysAspPheThrGlnMetSerGlnTyrPheLysAla                               300305310                                                                      CAGACGGAAGCTCGGAAACAGATGAGCAAGGAAGAGAAACTGAAAATC1192                           GlnThrGluAlaArgLysGlnMetSerLysGluGluLysLeuLysIle                               315320325                                                                      AAAGAGGAGAATGAAAAATTACTGAAAGAATATGGATTCTGTATTATG1240                           LysGluGluAsnGluLysLeuLeuLysGluTyrGlyPheCysIleMet                               330335340                                                                      GATAACCACAAAGAGAGGATTGCTAACTTCAAGATAGAGCCTCCTGGA1288                           AspAsnHisLysGluArgIleAlaAsnPheLysIleGluProProGly                               345350355                                                                      CTTTTCCGTGGCCGCGGCAACCACCCCAAGATGGGCATGCTGAAGAGA1336                           LeuPheArgGlyArgGlyAsnHisProLysMetGlyMetLeuLysArg                               360365370375                                                                   CGAATCATGCCCGAGGATATAATCATCAACTGTAGCAAAGATGCCAAG1384                           ArgIleMetProGluAspIleIleIleAsnCysSerLysAspAlaLys                               380385390                                                                      GTTCCTTCTCCTCCTCCAGGACATAAGTGGAAAGAAGTCCGGCATGAT1432                           ValProSerProProProGlyHisLysTrpLysGluValArgHisAsp                               395400405                                                                      AACAAGGTTACTTGGCTGGTTTCCTGGACAGAGAACATCCAAGGTTCC1480                           AsnLysValThrTrpLeuValSerTrpThrGluAsnIleGlnGlySer                               410415420                                                                      ATTAAATACATCATGCTTAACCCTAGTTCACGAATCAAGGGTGAGAAG1528                           IleLysTyrIleMetLeuAsnProSerSerArgIleLysGlyGluLys                               425430435                                                                      GACTGGCAGAAATACGAGACTGCTCGGCGGCTGAAAAAATGTGTGGAC1576                           AspTrpGlnLysTyrGluThrAlaArgArgLeuLysLysCysValAsp                               440445450455                                                                   AAGATCCGGAACCAGTATCGAGAAGACTGGAAGTCCAAAGAGATGAAA1624                           LysIleArgAsnGlnTyrArgGluAspTrpLysSerLysGluMetLys                               460465470                                                                      GTCCGGCAGAGAGCTGTAGCCCTGTACTTCATCGACAAGCTTGCTCTG1672                           ValArgGlnArgAlaValAlaLeuTyrPheIleAspLysLeuAlaLeu                               475480485                                                                      AGAGCAGGCAATGAAAAGGAGGAAGGAGAAACAGCGGACACTGTGGGC1720                           ArgAlaGlyAsnGluLysGluGluGlyGluThrAlaAspThrValGly                               490495500                                                                      TGCTGCTCACTTCGTGTGGAGCACATCAATCTACACCCAGAGTTGGAT1768                           CysCysSerLeuArgValGluHisIleAsnLeuHisProGluLeuAsp                               505510515                                                                      GGTCAGGAATATGTGGTAGAGTTTGACTTCCTCGGGAAGGACTCCATC1816                           GlyGlnGluTyrValValGluPheAspPheLeuGlyLysAspSerIle                               520525530535                                                                   AGATACTATAACAAGGTCCCTGTTGAGAAACGAGTTTTTAAGAACCTA1864                           ArgTyrTyrAsnLysValProValGluLysArgValPheLysAsnLeu                               540545550                                                                      CAACTATTTATGGAGAACAAGCAGCCCGAGGATGATCTTTTTGATAGA1912                           GlnLeuPheMetGluAsnLysGlnProGluAspAspLeuPheAspArg                               555560565                                                                      CTCAATACTGGTATTCTGAATAAGCATCTTCAGGATCTCATGGAGGGC1960                           LeuAsnThrGlyIleLeuAsnLysHisLeuGlnAspLeuMetGluGly                               570575580                                                                      TTGACAGCCAAGGTATTCCGTACGTTCAATGCCTCCATCACGCTACAG2008                           LeuThrAlaLysValPheArgThrPheAsnAlaSerIleThrLeuGln                               585590595                                                                      CAGCAGCTAAAAGAACTGACAGCCCCGGATGAGAACATCCCAGCGAAG2056                           GlnGlnLeuLysGluLeuThrAlaProAspGluAsnIleProAlaLys                               600605610615                                                                   ATCCTTTCTTATAACCGTGCCAATCGAGCTGTTGCAATTCTTTGTAAC2104                           IleLeuSerTyrAsnArgAlaAsnArgAlaValAlaIleLeuCysAsn                               620625630                                                                      CATCAGAGGGCACCACCAAAAACTTTTGAGAAGTCTATGATGAACTTG2152                           HisGlnArgAlaProProLysThrPheGluLysSerMetMetAsnLeu                               635640645                                                                      CAAACTAAGATTGATGCCAAGAAGGAACAGCTAGCAGATGCCCGGAGA2200                           GlnThrLysIleAspAlaLysLysGluGlnLeuAlaAspAlaArgArg                               650655660                                                                      GACCTGAAAAGTGCTAAGGCTGATGCCAAGGTCATGAAGGATGCAAAG2248                           AspLeuLysSerAlaLysAlaAspAlaLysValMetLysAspAlaLys                               665670675                                                                      ACGAAGAAGGTAGTAGAGTCAAAGAAGAAGGCTGTTCAGAGACTGGAG2296                           ThrLysLysValValGluSerLysLysLysAlaValGlnArgLeuGlu                               680685690695                                                                   GAACAGTTGATGAAGCTGGAAGTTCAAGCCACAGACCGAGAGGAAAAT2344                           GluGlnLeuMetLysLeuGluValGlnAlaThrAspArgGluGluAsn                               700705710                                                                      AAACAGATTGCCCTGGGAACCTCCAAACTCAATTTTCTGGACCCTAGG2392                           LysGlnIleAlaLeuGlyThrSerLysLeuAsnPheLeuAspProArg                               715720725                                                                      ATCACAGTGGCTTGGTGCAAGAAGTGGGGTGTCCCAATTGAGAAGATT2440                           IleThrValAlaTrpCysLysLysTrpGlyValProIleGluLysIle                               730735740                                                                      TACAACAAAACCCAGCGGGAGAAGTTTGCCTGGGCCATTGACATGGCT2488                           TyrAsnLysThrGlnArgGluLysPheAlaTrpAlaIleAspMetAla                               745750755                                                                      GATGAAGACTATGAGTTTTAGCCAGTCTCAAGAGGCAGAGTTCTGTGA2536                           AspGluAspTyrGluPhe                                                             760765                                                                         AGAGGAACAGTGTGGTTTGGGAAAGATGGATAAACTGAGCCTCACTTGCCCTCGTGCCTG2596               GGGGAGAGAGGCAGCAAGTCTTAACAAACCAACATCTTTGCGAAAAGATAAACCTGGAGA2656               TATTATAAGGGAGAGCTGAGCCAGTTGTCCTATGGACAACTTATTTAAAAATATTTCAGA2716               TATCAAAATTCTAGCTGTATGATTTGTTTTGAATTTTGTTTTTATTTTCAAGAGGGCAAG2776               TGGATGGGAATTTGTCAGCGTTCTACCAGGCAAATTCACTGTTTCACTGAAATGTTTGGA2836               TTCTCTTAGCTACTGTATGCAAAGTCCGATTATATTGGTGCGTTTTTACAGTTAGGGTTT2896               TGCAATAACTTCTATATTTTAATAGAAATAAATTCCTAAACTCCCTTCCCTCTCTCCCAT2956               TTCAGGAATTTAAAATTAAGTAGAACAAAAAACCCAGCGCACCTGTTAGAGTCGTCACTC3016               TCTATTGTCATGGGGATCAATTTTCATTAAACTTGAAGCAGTCGTGGCTTTGGCAGTGTT3076               TTGGTTCAGACACCTGTTCACAGAAAAAGCATGATGGGAAAATATTTCCTGACTTGAGTG3136               TTCCTTTTTAAATGTGAATTTTTTTTTTTTTTAATTATTTTAAAATATTTAAACCTTTTT3196               CTTGATCTTAAAGATCGTGTAGATTGGGGTTGGGGAGGGATGAAGGGCGAGTGAATCTAA3256               GGATAATGAAATAATCAGTGACTGAAACCATTTTCCCATCATCCTTTGTTCTGAGCATTC3316               GCTGTACCCTTTAAGATATCCATCTTTTTCTTTTTAACCCTAATCTTTCACTTGAAAGAT3376               TTTATTGTATAAAAAGTTTCACAGGTCAATAAACTTAGAGGAAAATGAGTATTTGGTCCA3436               AAAAAAGGAAAAATAATCAAGATTTTAGGGCTTTTATTTTTTCTTTTGTAATTGTGTAAA3496               AAATGGAAAAAAACATAAAAAGCAGAATTTTAATGTGAAGACATTTTTTGCTATAATCAT3556               TAGTTTTAGAGGCATTGTTAGTTTAGTGTGTGTGCAGAGTCCATTTCCCACATCTTTCCT3616               CAAGTATCTTCTATTTTTATCATGAATTC3645                                              (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 765 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        MetSerGlyAspHisLeuHisAsnAspSerGlnIleGluAlaAspPhe                               151015                                                                         ArgLeuAsnAspSerHisLysHisLysAspLysHisLysAspArgGlu                               202530                                                                         HisArgHisLysGluHisLysLysGluLysAspArgGluLysSerLys                               354045                                                                         HisSerAsnSerGluHisLysAspSerGluLysLysHisLysGluLys                               505560                                                                         GluLysThrLysHisLysAspGlySerSerGluLysHisLysAspLys                               65707580                                                                       HisLysAspArgAspLysGluLysArgLysGluGluLysValArgAla                               859095                                                                         SerGlyAspAlaLysIleLysLysGluLysGluAsnGlyPheSerSer                               100105110                                                                      ProProGlnIleLysAspGluProGluAspAspGlyTyrPheValPro                               115120125                                                                      ProLysGluAspIleLysProLeuLysArgProArgAspGluAspAsp                               130135140                                                                      ValAspTyrLysProLysLysIleLysThrGluAspThrLysLysGlu                               145150155160                                                                   LysLysArgLysLeuGluGluGluGluAspGlyLysLeuLysLysPro                               165170175                                                                      LysAsnLysAspLysAspLysLysValProGluProAspAsnLysLys                               180185190                                                                      LysLysProLysLysGluGluGluGlnLysTrpLysTrpTrpGluGlu                               195200205                                                                      GluArgTyrProGluGlyIleLysTrpLysPheLeuGluHisLysGly                               210215220                                                                      ProValPheAlaProProTyrGluProLeuProGluAsnValLysPhe                               225230235240                                                                   TyrTyrAspGlyLysValMetLysLeuSerProLysAlaGluGluVal                               245250255                                                                      AlaThrPhePheAlaLysMetLeuAspHisGluTyrThrThrLysGlu                               260265270                                                                      IlePheArgLysAsnPhePheLysAspTrpArgLysGluMetThrAsn                               275280285                                                                      GluGluLysAsnIleIleThrAsnLeuSerLysCysAspPheThrGln                               290295300                                                                      MetSerGlnTyrPheLysAlaGlnThrGluAlaArgLysGlnMetSer                               305310315320                                                                   LysGluGluLysLeuLysIleLysGluGluAsnGluLysLeuLeuLys                               325330335                                                                      GluTyrGlyPheCysIleMetAspAsnHisLysGluArgIleAlaAsn                               340345350                                                                      PheLysIleGluProProGlyLeuPheArgGlyArgGlyAsnHisPro                               355360365                                                                      LysMetGlyMetLeuLysArgArgIleMetProGluAspIleIleIle                               370375380                                                                      AsnCysSerLysAspAlaLysValProSerProProProGlyHisLys                               385390395400                                                                   TrpLysGluValArgHisAspAsnLysValThrTrpLeuValSerTrp                               405410415                                                                      ThrGluAsnIleGlnGlySerIleLysTyrIleMetLeuAsnProSer                               420425430                                                                      SerArgIleLysGlyGluLysAspTrpGlnLysTyrGluThrAlaArg                               435440445                                                                      ArgLeuLysLysCysValAspLysIleArgAsnGlnTyrArgGluAsp                               450455460                                                                      TrpLysSerLysGluMetLysValArgGlnArgAlaValAlaLeuTyr                               465470475480                                                                   PheIleAspLysLeuAlaLeuArgAlaGlyAsnGluLysGluGluGly                               485490495                                                                      GluThrAlaAspThrValGlyCysCysSerLeuArgValGluHisIle                               500505510                                                                      AsnLeuHisProGluLeuAspGlyGlnGluTyrValValGluPheAsp                               515520525                                                                      PheLeuGlyLysAspSerIleArgTyrTyrAsnLysValProValGlu                               530535540                                                                      LysArgValPheLysAsnLeuGlnLeuPheMetGluAsnLysGlnPro                               545550555560                                                                   GluAspAspLeuPheAspArgLeuAsnThrGlyIleLeuAsnLysHis                               565570575                                                                      LeuGlnAspLeuMetGluGlyLeuThrAlaLysValPheArgThrPhe                               580585590                                                                      AsnAlaSerIleThrLeuGlnGlnGlnLeuLysGluLeuThrAlaPro                               595600605                                                                      AspGluAsnIleProAlaLysIleLeuSerTyrAsnArgAlaAsnArg                               610615620                                                                      AlaValAlaIleLeuCysAsnHisGlnArgAlaProProLysThrPhe                               625630635640                                                                   GluLysSerMetMetAsnLeuGlnThrLysIleAspAlaLysLysGlu                               645650655                                                                      GlnLeuAlaAspAlaArgArgAspLeuLysSerAlaLysAlaAspAla                               660665670                                                                      LysValMetLysAspAlaLysThrLysLysValValGluSerLysLys                               675680685                                                                      LysAlaValGlnArgLeuGluGluGlnLeuMetLysLeuGluValGln                               690695700                                                                      AlaThrAspArgGluGluAsnLysGlnIleAlaLeuGlyThrSerLys                               705710715720                                                                   LeuAsnPheLeuAspProArgIleThrValAlaTrpCysLysLysTrp                               725730735                                                                      GlyValProIleGluLysIleTyrAsnLysThrGlnArgGluLysPhe                               740745750                                                                      AlaTrpAlaIleAspMetAlaAspGluAspTyrGluPhe                                        755760765                                                                      (2) INFORMATION FOR SEQ ID NO:3:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 24 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: other nucleic acid                                         (A) DESCRIPTION: /desc = "PR1 primer of Scl-70"                                (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                        GATCCTAGGGTCCAGAAAATTGAG24                                                     (2) INFORMATION FOR SEQ ID NO:4:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 24 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: other nucleic acid                                         (A) DESCRIPTION: /desc = "PF1 primer of Scl-70"                                (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                        AAGGAACAGCTAGCAGATGCCCGG24                                                     (2) INFORMATION FOR SEQ ID NO:5:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 17 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: other nucleic acid                                         (A) DESCRIPTION: /desc = "N8 primer"                                           (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                        CTTGCAAACTAAGATTG17                                                            (2) INFORMATION FOR SEQ ID NO:6:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 24 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: other nucleic acid                                         (A) DESCRIPTION: /desc = "PR2 primer of Scl-70"                                (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                        CCGGGCATCTGCTAGCTGTTCCTT24                                                     (2) INFORMATION FOR SEQ ID NO:7:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 24 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: other nucleic acid                                         (A) DESCRIPTION: /desc = "PF2 primer of Scl-70"                                (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                        AAGGTATTCCGTACGTTCAATGCC24                                                     __________________________________________________________________________ 

What is claimed is:
 1. A mutant human DNA topoisomerase I protein comprising the amino acid sequence from the 96th through the 590th of the amino acid sequence described in SEQ ID No.:1.
 2. A mutant of human DNA topoisomerase I protein comprising the amino acid sequence from the 591st through the 765th of the amino acid sequence described in SEQ ID No.:1.
 3. A mutant human DNA topoisomerase I protein as claimed in claim 2 wherein the amino acid at the 723rd position is tyrosine.
 4. A mutant human DNA topoisomerase I protein comprising the amino acid sequence from the 96th through the 765th of the amino acid sequence described in SEQ ID No.:1.
 5. A mutant human DNA topoisomerase I protein as claimed in claim 4 wherein the amino acid at the 723rd position is tyrosine.
 6. A mutant human DNA topoisomerase I protein comprising the amino acid sequence from the 542nd through the 765th of the amino acid sequence described in SEQ ID No.:1.
 7. A mutant human DNA topoisomerase I protein as claimed in claim 6 wherein the amino acid at the 723rd position is tyrosine.
 8. A mutant human DNA topoisomerase I protein comprising the amino acid sequence from the 1st through the 765th of the amino acid sequence described in SEQ ID No.:1.
 9. A mutant human DNA topoisomerase I protein as claimed in claim 8 wherein the amino acid at the 723rd position is tyrosine.
 10. A mutant human DNA topoisomerase I protein comprising the amino acid sequence from the 1st through the 765th of the amino acid sequence described in SEQ ID No.:1, in which the amino acids at the 592nd position and 723rd position are both lacking.
 11. A method of detecting an autoantibody comprising:a) contacting the protein as claimed in any one of claims 1 2, 4, 6, 8, and 10 with sera from a patient; and b) measuring the autoantibody in an immunoassay.
 12. A method of detecting an autoantibody comprising:a) contacting the protein as claimed in claim 3 with sera from a patient; and b) measuring the autoantibody in an immunoassay.
 13. A method of detecting an autoantibody comprising:a) contacting the protein as claimed in claim 5 with sera from a patient; and b) measuring the autoantibody in an immunoassay.
 14. A method of detecting an autoantibody comprising:a) contacting the protein as claimed in claim 7 with sera from a patient; and b) measuring the autoantibody in an immunoassay.
 15. A method of detecting an autoantibody comprising:a) contacting the protein as claimed in claim 9 with sera from a patient; and b) measuring the autoantibody in an immunoassay.
 16. A mutant human DNA topoisomerase I protein comprising an amino acid sequence from the 542nd amino acid through the 592nd amino acid of the amino acid sequence described in SEQ ID NO:1.
 17. A mutant human topoisomerase I protein comprising an amino acid sequence from the 542nd amino acid through the 592nd amino acid of the amino acid sequence described in SEQ ID NO: 1, wherein the amino acid at the 592nd position is lacking.
 18. A mutant human DNA topoisomerase I protein comprising an amino acid sequence from the 1st through the 765th amino acid of the amino acid sequence described in SEQ ID NO:1, in which one amino acid at the 592nd position is lacking and the amino acid at the 723rd position is replaced with tyrosine.
 19. A method of detecting an autoantibody comprising:a) contacting the protein as claimed in any one of claims 16, 17, and 18 with sera from a patient; and b) measuring the autoantibody in an immunoassay. 